No, both manifest v2 and v3, but in earlier versions add-ons had to be vetted by reviewers or manually added to their account collections by users, but from v121,all extensions marked by their devs as compatible are available to everyone https://blog.mozilla.org/addons/2023/11/28/open-extensions-on-firefox-for-android-debut-december-14-but-you-can-get-a-sneak-peek-today/

Yes, Predirect currently chooses randomly from list of instances from farside/official(I’ll make it updatable/refreshable in near future) or one custom instance (I’ll also add editing list of custom instances in far future) [ofc if chrome store allows these two]. I didn’t add libredirect/reddit due to ratelimiting problems and GotHub, anonymous overflow due to usability issues. I’ll add search, maps in near future and also others. Predirect does distribute traffic by randomising instances so not an issue. Thanks for suggestions and contributions are welcome for any of these